There is an image of this cultivar on the Hosta Library. From the photo on the HL website, it appears to be a very upright, large size hosta with green leaves and light creamy yellow marginal variegation and red dotted petioles. This non-registered cultivar was originated in Japan. 

Mikiko Lockwood in an article on The Hosta Library titled, A Little About Japanese Hosta Terms defines the term iwa as rock, Iwa Gibōshi or H. longipes, the term fukurin as margined or edged. and the term urajiro as white-backed or white underside.